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Gravitational slingshot as a weapon

  1. Oct 3, 2009 #1
    Since we use the gravitational slingshot to accelerate spacecraft essentially without fuel, could that be used to put a large rock into a solar orbit at a high enough velocity to be a weapon? It seems to me we have the technology to make a weapon like this in an orbit that can be nudged slightly at the right time to impact the earth where we want with a lot more destructive force than a nuclear weapon.
  2. jcsd
  3. Oct 4, 2009 #2

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    First, there is no military application for a bigger bomb. The largest bombs in the cold war had theoretical yields of 100 megatons. Today I believe the largest single warhead in the US stockpile is 1.2 MT, and most are closer to 300 kT.

    Second, if your object is near earth all the time, so you can deploy it when you want to, it has to have a low relative velocity. If you want it to have a high relative velocity, it's only near the earth rarely and you can't fire it except in a few narrow time windows. It could easily be years between the time you fire it and the time of impact, which makes it completely useless in fighting a war.
  4. Oct 4, 2009 #3
    No military application for a bigger bomb? The reason that they don't have bigger bombs is because nuclear weapons aren't much more effective when bigger, there is more fallout and we can make more smaller ones. By your reasoning there would be no need need for nukes at all because they are bigger than conventional weapons.

    If it didn't have the higher velocity it wouldn't be much use. No, it wouldn't be useful in a war unless the war was protracted and what wars are protracted? Hmmm, all of them?

    It would have a use as a threat. It would have a use as a first strike weapon. It would have a use as a revenge weapon. It would make the biggest nukes look tiny and no fallout to haunt the user. The estimated diameter of the meteor that hit Arizona is only 54 yards. We couldn't make a nuke big enough to do the damage that meteor did. Better yet, it might even be able to be done without revealing who did it. Taking it a little further, if we knew how to replicate the air burst that happened over Tanguska it would be an incredibly destructive weapon in three flavors, rocky road, sherbet and iron nougat.

    Then there is the morality question. Maybe the US wouldn't consider using a weapon like that on ethical grounds but the technology, if possible, will be available to other countries sooner or later if it isn't already and there are other countries who don't have ethical problems with ANY weapon. If we can do it, how long before China or Russia can? You think they wouldn't if they could? Let me know when the arms race is over and I will admit the idea is useless.
    Last edited: Oct 4, 2009
  5. Oct 4, 2009 #4

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    I'll let you look up nuclear yields vs. time and see for yourself - bombs are not getting larger and larger.

    I maintain that a weapon that takes many years - perhaps 20 - to strike its target is militarily useless. Germany and Japan were the US' enemies in 1945. They were US allies in 1950.
  6. Oct 4, 2009 #5
    We could, but it'd be pointless. In theory a fusion bomb has no larger limit on size and thermonuclear reactions pack about a million times the energy of meteorites into the same mass. Triggering such reactions can be tricky, but there's nothing technically impossible about 1,000 megaton or 10,000 megaton bombs. There are delivery issues however, since they would mass many tons, making them utterly useless to put on an ICBM. Nuclear warheads typically have low yields so they can be packed into small independent warheads to make interception harder. While the US didn't bother deploying its threatened total coverage ABM system in the early 1970s the (former) USSR did deploy some interceptors around Moscow.
  7. Oct 4, 2009 #6


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    I am at war with my neighbour. I have planted some seeds of oak trees next to our mutual fence. If he gives me a hard time, I'm going to water them continually until they grow big enough to destroy his backyard.

    I have told him this, and I am now confident that he will be a better neighbour, lest I unleash my weapon on him.

    fiilindablank (if you're still around), you have a naive view of the motivators and practicalities of arms races. It just doesn't work the way you imagine it does.
  8. Oct 4, 2009 #7
  9. Oct 6, 2009 #8


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    It actually takes a lot of fuel to line up a slingshot. The payoff is that you get a higher delta V than if you didn't perform the slingshot. But you've already spent a lot of delta V getting in position.

    A 50 meter asteroid is a LOT more massive than anything we've ever put in space. To change its velocity by even 1 m/s would require a lot of energy. And unless we conveniently found a 50 meter rock that was on a near-impact trajectory, we'd need to change its velocity by a lot more than that, or change it decades in advance of the planned impact.

    Then there's the issue of precision. Did the asteroid behave exactly how you expected. Or did you accidently target your own country?
  10. Oct 6, 2009 #9
    Oh what fun! There's always an application for a bigger bomb. Turns out that huge nuclear bombs simply don't scale well for both economic and tactical reasons that may not directly apply to a death comet that may require no nuclear material and travel at high enough speeds so as to be virtually unstoppable. It requires a lot more material to make larger nukes, and much of the additional energy of their detonation is simply lost to space. It makes a lot more sense to spread that material over a lot of smaller bombs to yield more destructive force per pound of fissionable material and get more chances to evade countermeasures and hit targets. Do a quick google search on "Tsar Bomb"

    Your second point is easily countered. if you can make one orbital death comet, you can make 100 or 1000. Launch one a day for the duration of the orbit that you choose, and by the end of the first death comet's orbit, you'll be ready to deal down death daily! What could go wrong!

    I suspect a more compelling reason why this is a terrible idea is the immense cost of launching fuel and rocks from the earth's surface for even one death comet, or of exploring the neighborhood around Earth to find suitable projectiles. The world can barely afford to keep the ISS in orbit. Death comets would be tough sell when the United States (or the Russians or the Chinese) already have enough nukes to destroy everything.
  11. Oct 6, 2009 #10


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    OP was banned and the question was answered, so there is nothing more to discuss here. Thread locked.
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